720 SPECIAL PHYSIOLOGY. 



retarding influence of the addition of saline solutions, are not well ex- 

 plained ; they may operate, simply by altering the specific gravity, and 

 also the viscosity of the blood. The retardation, or prevention, of 

 coagulation, by the addition of ammonia, even if transmitted through 

 the blood in the form of vapor, the occurrence of coagulation in such 

 blood when the ammonia escapes, and its resumption of the fluid state 

 on the introduction of fresh ammoniacal vapor phenomena which can 

 be reproduced several times over, in the same blood are the chief 

 facts adduced, together with the known presence of ammonia in the 

 halitus of the blood, in favor of the hypothesis of Dr. Richardson, that 

 the ammonia is the cause of the fluidity of the blood in the body, and 

 its escape, the immediate occasion of coagulation in drawn blood. 



The mode of action of narcotic and sedative poisons, is not under- 

 stood. The more rapid coagulation of the blood in feeble states of the 

 system, does not depend upon an increased quantity of the fibrin or coag- 

 ulating substance, but rather on the dilute or watery condition of the 

 blood. On the other hand, the more slowly coagulating blood of the 

 inflammatory state is accompanied by an actual increase in the quantity 

 of fibrin, though there appears, possibly from the high specific gravity 

 and richness of the blood, to be a greater resistance to the act of coag- 

 ulation. The necessity for perfect smoothness of the interior of the 

 heart and bloodvessels, in order to prevent coagulation, may be inferred 

 from the highly polished character of their epithelial lining ; the influence 

 of rough surfaces in their interior, in determining coagulation of the 

 blood, is shown by the small coagula formed upon excrescences of the 

 valves of the heart, and by the flakes of fibrin which collect on atherom- 

 atous or calcified portions of vessels in the rough interior of aneurisms, 

 and at the openings of lacerated vessels, which are so much sooner 

 closed by coagula, than those which are cleanly cut. Coagula have 

 been induced experimentally in animals, in the interior of large vessels, 

 by the passage of needles, wires, or threads, into such vessels ; when 

 formed in an artery, the coagulum is firm and elongated in the direction 

 of the blood current, whilst, in the veins, the clots are loose and massive. 

 In certain cases, during life, especially during the last hours of life, 

 such coagula may form in the living blood, especially when rough ex- 

 crescences exist on the valves of the heart. The influence of an inflamed 

 condition of the coats of the bloodvessels, in causing coagulation of the 

 fibrin, has been referred to the partial loss of vitality, or to the inter- 

 ruption of the vital processes, in the inflamed tissue, by which it is, so 

 far, approximated to the state of inanimate matter. The injection of 

 pus, the pulpy substance of the brain, and other semisolid matters, 

 into the bloodvessels of an animal, rapidly coagulates the blood, a result 

 probably attributable to the effects of contact with the multiplied sur- 

 faces of non-living matter. 



Blood confined in a living vein between two ligatures, retains its 

 fluidity for a long time, beginning to coagulate commonly after from 

 3 to 5 hours, and sometimes even being only imperfectly clotted at the 

 end of 24 hours, though such blood will coagulate in a few minutes 

 when withdrawn from the living vein. If the vein be dead, although 

 the blood is equally well excluded from the air, coagulation takes place 



